A complex, multi-year project is winding down along a portion of the Cedar River where, for decades, chronic flooding threatened dozens of residents, and where the quality of fish and wildlife habitat was greatly diminished by the river’s restricted channel.

Over time, levees built along Rainbow Bend isolated the Cedar River from its floodplain, which resulted in a river with reduced benefits to its native fish and wildlife populations, but also in a river with the potential for fast and erosive flows that required ongoing maintenance to keep erosion in check.

“Reconnecting the Cedar River to part of its historic floodplain lowers the threat of flooding to everyone who lives downstream, improves habitat for fish and wildlife, and protects a nearby highway and trail,” said King County Executive Dow Constantine. “More than a decade of steady work is coming to fruition.”

The project has been accomplished through a partnership involving King County, the King County Flood Control District, the City of Seattle and the Lake Washington/ Cedar/Sammamish Watershed Resource Inventory Area (WRIA 8)

Taking out the old river levee and returning the Cedar River to a 40-acre swath of its historic floodplain at Rainbow Bend eases the flood threat to downstream residents and nearby State Route 169, as well as King County’s popular Cedar River Trail.

Because of the significant habitat benefits for imperiled chinook salmon and other species, the project has long been a high-priority in both the Lake Washington/ Cedar/Sammamish Watershed Chinook Salmon Conservation Plan and the King County Flood Hazard Management Plan.

The work was done in phases beginning more than a decade ago, and included purchasing a flood-prone mobile home park and 10 single-family homes from their owners, as well as paying to relocate rental tenants.

Safely relocating people out of harm’s way cleared the path for King County to remove the flood-prone homes and a degraded, 900-foot-long levee. These actions gave the Cedar River the ability to reconnect to the floodplain, which provided the dual benefits of restoring habitat and also giving floodwaters a place to fan out and lose their destructive force.

The habitat restoration work included excavating “pilot channels” where the Cedar River can readily access the newly available floodplain, and placing logs on the floodplain to help create more-diverse habitat.

“Returning the Cedar River to its larger floodplain will have significant benefits to salmon and the surrounding habitat,” said Larry Phillips, King County Council representative to the WRIA 8 Salmon Recovery Council and Chair of the Cedar River Council. “Removing the old levee will allow the river and its landscapes to form natural side-channel habitat for salmon and channel migration across the floodplain that will create a more diverse and resilient river through this area.”

Chinook salmon in the Cedar River, which have protection under the federal Endangered Species Act, are expected to benefit from the additional habitat – particularly new areas where young fish can feed and escape predators.

The project will also benefit other fish species, including sockeye salmon, coho salmon, and steelhead and cutthroat trout.

The Cedar River is expected to change course through the now-available floodplain. King County will monitor this site closely in the coming years to ensure the project is performing as desired, and to better understand how fish and wildlife respond to restoration on this scale.

The Rainbow Bend project was developed, implemented and funded by a team of organizations, and included state Salmon Recovery Funding Board and Puget Sound Acquisition and Restoration funds directed by WRIA 8, plus funding from the City of Seattle’s Cedar River Watershed Habitat Conservation Plan, King County, King County Conservation Futures, the King County Flood Control District, King Conservation District, and the Federal Emergency Management Agency.

Learn more about the project at http://www.kingcounty.gov/environment/wlr/sections-programs/river-floodplain-section/capital-projects/rainbow-bend.aspx.